Utility lines are generally supported by two types of crossarms - tangent crossarms (generally referred to as "crossarms") and deadend crossarms (generally referred to as "deadends"). Tangent crossarms are used to support a generally vertically downward load resulting from the weight of the utility lines. In the most common arrangement, the utility line is supported by an insulator which in turn is vertically connected to the crossarm. Deadends, on the other hand, are used to support a generally horizontal load to maintain tension in the utility line. In the most common arrangement, the utility line is attached to an insulator which in turn is horizontally connected to the deadend. A single deadend may be employed at a terminal end, or two deadends may be employed adjacent one another on the same utility pole in order to maintain the line tension in both directions. In the latter configuration, "jumper lines" are typically used to interconnect the utility lines attached to the two deadends in order to provide a continuous transmission. Deadends are employed when it is necessary to make a for example 90 degree turn in the utility lines, and are also used periodically in straight sections for the purpose of maintaining utility line tension.
The vast majority of crossarms and deadends currently in service are made of wood, although some are manufactured from steel or aluminum. Wood support beams, however, suffer from several disadvantages. The main disadvantage is the weatherability of wood beams. Even when treated, wood beams will tend to rot over a period of time, thus requiring relatively frequent replacement. This is especially true in warmer and more humid climates such as the southern United States, where the service life of wood beams is a fraction of that in colder climates. Moreover, rotting of wood beams tends to decrease the strength of the beam over its life, which could lead to premature failure. The frequency with which wood beams must be replaced as a result of premature weathering has a number of drawbacks, including increased labor costs, disposal costs, and the added risk of injury to linemen. Another concern with wood beams is that they are a relatively poor insulator, particularly when damp. This not only results in loss of electricity traveling through the beam and down the utility pole, but also poses a hazard for utility linemen. For example, if a lineman were to touch a "hot" electrical line and a wood beam, he could be electrocuted because the beam would provide a ground. Metal support beams suffer from similar disadvantages, such as weatherability problems due to corrosion and the fact that metal support beams are highly conductive.
Pultruded fiberglass support beams solve many of the problems associated with wood or metal beams. They have a high strength to weight ratio and are very good insulators. When treated with an ultraviolet protective coating, fiberglass beams can last as much as five to ten times longer than their wood counterparts. The strength of pultruded beams also does not decrease substantially over their life span as do wood beams. Moreover, pultruded beams can be manufactured at a cost which is very competitive with, and possibly even less than, wood or metal beams.
Prior art pultruded support beams, however, suffer from certain disadvantages as well. One problem relates to moisture entering the beam and acting as a conductor, which can result in "arcing". Arcing is a concern both because of the potential for electricity loss and because of lineman safety considerations. Another problem associated with pultruded beams is that compression damage or "crushing" of the beam can occur when tightening mounting bolts or insulator bolts. This is especially a problem because linemen are accustomed to mounting wood beams, where there is no such concern.
One prior art construction attempting to solve these problems is a hollow pultruded beam which is completely filled with a foam, such as polyurethane foam. It has been found, however, that the foam neither fully prevents moisture from entering the beam nor provides adequate axial strength to prevent compression damage. Also, this foam-filled hollow beam design is relatively expensive to manufacture.
U.S. Pat. No. 3,715,460 represents another attempt to solve these problems. This patent discloses a deadend support beam comprising a fiberglass tube with metallic mounting members attached to opposite ends to be engaged with line insulators. The compression damage problem is solved through the tube having a very high wall thickness, but this is accomplished at the expense of significant added cost in terms of materials and manufacturing. As to the arcing problem, the metallic mounting members do not appear to adequately prevent moisture from entering the beam due to the fact that they are also used to support the perpendicular load applied by the attached insulator. This creates the significant possibility that the seal between the mounting members and the tubular beam will be broken as a result of the perpendicular load, thus allowing moisture to enter the beam. In addition, the mounting bolts extending through transverse holes in the beam do not seal the holes and therefore do not appear to prevent moisture from entering the beam.
Another prior art attempt to solve these problems is shown in U.S. Pat. No. 4,262,047. In this construction, the beam comprises an outer covering bonded around a fiberglass honeycomb log having adjacent cells throughout the log. While this design reduces concerns about arcing and may provide sufficient axial strength to prevent compression damage, this is accomplished through a very complex, expensive and difficult to manufacture construction.
Another problem with utility line support beams arises when attempting to mount beams with a non-standard transverse dimension due to noncompatibility with standard hardware or tooling. For example, in the United States, the hardware used in the field is made to attach to a typical 3.5 inch by 4.5 inch wood beam. Therefore, such tools could not be used if the beam is of a substantially smaller dimension, requiring either use of specially designed tools or increasing the size of the beam to the standard dimension when it is not structurally necessary. Both of these solutions, however, involve substantial additional cost.
What has been needed is a simple, low cost and easy to manufacture pultruded utility line support beam that prevents moisture from entering the beam and the attendant potential for arcing, and that has sufficient axial strength to prevent compression damage. What is also needed is a simple and low cost method for adapting a utility line support beam having a non-standard dimension to be mounted using standard-sized hardware or tooling.